This invention relates to power supplies that furnish DC voltages and DC currents to integrated circuits in data processing apparatus such as computers and peripherals; and more particularly, it relates to systems of several intercoupled power supplies which operate in parallel to share in furnishing the DC current.
Basically, a power supply of the above type receives AC power from a wall outlet, and it converts that AC input power to DC output power. In one typical power supply, the Ac input power is at 208 volts and 60 Hz, while the DC output power is at 5 volts. Each power supply has a maximum power rating which determines how much current it can furnish and still maintain the DC voltage within a certain regulation band. For example, a 1500 watt, 5 volt power supply can furnish up to 300 amps and still maintain a 5 volt DC output voltage.
Frequently, DC power is furnished to the circuits of data processing apparatus by just one large power supply. However, a system of several small power supplies operating in parallel can also be employed. Suppose, for example, that the data processing apparatus requires 4500 watts at 5 volts. This can be achieved by one 4500 watt, 5 volt power supply which furnishes 900 amps, or it can be achieved by a system of three 1500 watt, 5 volt power supplies which operate in parallel and furnish 300 amps each.
If a single large power supply is used, then the total number of power supply parts will generally be minimized. Also, the total number of connections which need to be made in order to install the power supply in the data processing apparatus will generally be minimized.
But when a system of several small power supplies is used, the individual supplies can be arranged to fit into differently shaped spaces within the data processing apparatus. Also, it generally is easier to circulate air through several small power supplies rather than one large power supply, and thus cooling the smaller power supplies may be easier. Further, with small power supplies, it generally is easier to shorten the distance which large currents must travel; and thus it is easier to reduce inductive noise in the power supplies' output voltage.
One problem, however, with systems of paralleled power supplies in the prior art is that individual supplies in the system could not be separately turned off and turned back on without causing the DC output voltage of the system to go outside of its regulation band. But such a feature is very desirable because it enables any one power supply in the system to become defective, to be automatically turned off, to be replaced, and to be turned back on without ever stopping the operation of the data processing apparatus.
Accordingly, a primary object of the invention is to provide a system of parallel power supplies in which the above problem is overcome.